Impact hammer mill



y 1954 D. R. TULLIS 2,678,169

\ V IMPACT HAMMER MILL Filed April 17', 1951 Patented May 11, 1954 UNITED STATES TENT OFFICE This invention relates to impact hammer mills for grinding purposes of the type including a casing and mounted within the casing, a rotor to which are pivoted knife blades, the casing also containing a perforated or open-mesh, screen from which ground material is discharged to an outlet duct.

When dried grass, grass meal or grain is ground in a mill of the type referred to, the fibrous part of the grass takes a very much longer time to grind than the non-fibrous portion and the carbohydrate portion. The difference may amount to a ratio of 5:1 so that in the ordinary course of continuous grinding which is the normal practice, the actual rate of output of the mill in cwts. per hour is controlled by the rate at which it can grind the fibrous part of the grass to a degree which is sufficieritly fine to pass through the screen. In other words and in actual practice, the more easily ground portion passes quickly through the screen and leaves behind in increasing amounts the fibrous or slowly grindable portion until the output of the mill is diminished to the rate at which it can grind the fibrous portion of the grass. Such fibrous matter ultimately clogs the mill.

An object of the present invention is to provide means for removing the fibrous matter from the mill.

In an impact hammer mill of the type referred to according to the invention there are incorporated a deflecting device movable close to the path followed by the tips of the knife-blades, a closable aperture in the casing, the deflecting device and the aperture being so located relatively to one another that material impelled by the knife-blades against the deflecting device is diverted through the aperture, and a back pressure valve located in the outlet duct.

Automatic timing means may be fitted to swing the deflecting device towards the blades and to open the aperture simultaneously or consecutively at predetermined intervals. Alternatively, since unground grass or grass meal is dark green in colour, whereas the fibrous matter is pale yellow in colour by reflected light,,photo-electrio means sensitive to the difference in colour may be provided to operate the deflector plate and the back pressure valve automatically when the proportion of fibrous matter in the mill increases to more than a desired proportion i. e. when the contents of the mill change colour.

A practical embodiment of the invention is illustrated in the accompanying drawings in which Fig. 1 is a side elevation of a mill with one of the end plates removed, and Fig. 2 is a section of the mill through the vertical plane con taining the axis of the shaft.

In the drawings, 5 denotes a casing and 2 denotes a rotor to which are pivoted knife blades 3. i denotes a perforated screen, and 5 denotes an outlet pipe from the space enclosed by the casing l and the screen l. 6 denotes a feed chute. i denotes a deflecting device in the form of an aerofoil pivoted to the casing i. t denotes an aperture in the casing l closable by a flap 9. it denotes a back pressure valve in the outlet pipe 5, and M denotes an elevating fan at the discharge end of the pipe 5.

In practice, when dried grass or grass meal fed to the mill through the feed chute 6 is ground to powder in the mill, it passes through the screen 6i into the outlet pipe is. The fibrous matter, however, cannot pass so quickly through the screen i and is whirled around with the blades 3. To remove the fibrous matter, the defleeting device 2' is swung towards the path followed by the knife blades 3, thereupon occupying the position illustrated by the dotted lines, the flap s is swung to open the aperture 8, and the back pressure valve til is partly or completely closed to cause the pressure in the easing to increase. The fibrous matter, in moving outwards from the blades 3 by centrifugal action, is entrained by the deflecting device 1 and directed towards the aperture 8 through which it is thrown, the expelling action being accelerated by the increased pressure in the casing l consequent on the closure of the back pressure valve it.

It will actually be found that as compared with prior constructions the mill will produce a much greater output per hour of the more edible and more digestible portions of the grass so treated. This increase of output is the more noticeable as the screen size is reduced, and indeed it will be noticed that, although a finer screen is fitted, the output will remain as high as it was when a much coarser screen is used, with the added advantage that effective fibre separation can be accomplished without loss of output.

The same effect will be noticed when grinding dried grass or green hay of high fibre content which, upon being ground continuously through a mill not fitted with the above devices, may show on analysis a fibre content of 3036% whereas, when the same material is ground through the same mill fitted with the above devices it will show an analysis of only 15-20% fibre and 3 thus be raised to the quality of a high grade grass meal. Fibre content can be reduced still further according to the condition of the grass or hay before it is fed to the mill.

What is claimed is:

1. An impact hammer mill for grinding fibrous materials such as dried grass, hay and grain, comprising a casing having a feed chute opening thereinto for supplying material to the upper part of the casing, the casing having an aperture in its upper portion for the discharge of fibrous material, a movable closure for said apertures, rotor mounted in said casing, knife blades pivoted to said rotor, a foraminous screen disposed.

within said casing around at least the lower portion of said rotor outside the path'followed'by the tips of the knife blades, saidscreen being adapted to pass finely ground materiaLa discharge outlet pipe connected into the lower part of the casing for receiving the finely ground material discharged by the screen, a suction fan connected into the discharge end of said pipe for drawing air into the casing through the chute opening and for withdrawing finely ground material from the casing, a deflecting device disposed within the upper part of the casing outside the path of the tips of said knife blades and movable-close to the path followed by the tips of said knife blades, said deflecting device and said discharge aperture for fibrous materials being so located relative to each other that fibrous material impelled'by said knife blades against said deflecting device, when'said closure is opened and said device is moved close to the path followed by-the-tips of the knife blades, is diverted by said deflecting device through said discharge aperture'for fibrous-material, means for moving said deflecting device toward and away from the tipsofjtheknife blades, and a back pressure va lve'located in; said outlet pipe for'cutting off the flow of airtherethrough when said closure for the aperture is opened and said deflecting de- '2, in which said aperture extends opposite to and the full length of the rotor, and said deflecting device is located in front of the aperture so that whenfibrous material is discharged it flows over.v the upper surface of said device into the aperture.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 448,844 Burnham et a1 Mar. 24, 1891 1,008,242 Cooke Nov. 7, 1911 1,201,901 West Oct. 17, 1916 1,241,749 McCool Oct. 2, 1917 1,698,753 Knittel Jan. 15, 1929 1,755,573 Clement Apr. 22, 1930 1,915,920 Campbell June 27, 1933 1,955,255 Sengstaken Apr. 17, 1934 2,105,759 Stevenson Jan, 18, 1938 2,233,728 Bell V Mar. 4, 1941 2,309,326 Miller, Jan. 26, 1943 2,588,865 Moldenhauer Mar. 11, 1952 V FOREIGN PATENTS Number Country V Date V 235,955 V GreatBritain. June 26, 192.5. 289,319 7 Italy Oct.13, 1931 

